The present invention relates to an FRP (fiber reinforced plastic) plate, i.e., a spring member having spring characteristics which consists of a number of reinforcing fibers which are impregnated with and held in a thermosetting resin, and to a process for manufacturing the same.
An FRP plate is suitable for a laminated or leaf spring since it is light in weight and has high strength and elasticity due to the presence of the reinforcing fibers embedded therein. The direction along which the reinforcing fibers extend and the arrangement of these fibers in an FRP laminated spring are determined in accordance with the type of resin used, the application and operating conditions of the spring. Although an FRP spring has various good properties such as light weight and good corrosion resistance as described above, there is still room for improvement.
First, when the surface of an FRP plate is damaged for some reason or reinforcing fibers are severed at portions close to the surface of the plate due to repeated load, the plate tends to crack or separate in the direction along which the fibers extend. When an FRP plate is subjected to a surface treatment such as polishing or cleaning for adhering another part thereto, portions of reinforcing fibers are often exposed or severed, degrading the strength of teh plate.
Second, the reinforcing fibers of an FRP plate have great tensile strength but easily buckle under a compression force. Accordingly, a laminated spring comprising an FRP plate is weak in the direction along which a compression force acts, and therefore has a poor overall durability.